Retrograde menstruation happens when tissue that lines the inside of your uterus flows out in the wrong direction during the period—through the fallopian tubes. While this process can occur in many healthy women as well, women with endometriosis experience it differently. The out-of-place tissue can attach and start growing on surfaces and organs in the pelvic region. This can cause pain and inflammation.
Other possible theories on what causes endometriosis include:
Watch this video to learn about the inner workings of endometriosis and why it hurts.
Scientists aren't sure, but some possible endometriosis risk factors include:
No one demographic or ethnicity has been labeled as a risk factor for endometriosis.